Topical application of medication in the form of dermally applied cremes is commonplace. Numerous non-prescription products containing methyl salicylate, hydrocortisone, lidocainehydrochloride, or benzocaine may be purchased off the shelf at any drug store. In these cremes, the active ingredient is mixed with water and assorted high molecular weight waxes and emulsifiers, such as propylene glycol, lanolin, stearic acid, and ethyl alcohol, to form a creme which can be rubbed into the skin. Also known are iontophoresis, the introduction of various ions through the skin by electricity, and phonophoresis which is the transdermal introduction of substance into the body by means of ultrasound. However, iontophoresis has always used sponges or the like soaked in medicated water to provide the source of the transfer medicants whereas phonophoresis has used cremes.
Hydrogels are also well known and have been used in conjunction with medical electrodes. U.S. Pat. No. 4,706,680 issued Nov. 17, 1987 lists numerous patents which disclose hydrophilic gels and medical electrodes employing them. However, none of these patents appear to be directed to a chemically crosslinked hydrogel wherein the crosslinking agent also is the electrical conductivity agent.